(1) Field of the Invention
The present invention relates to a compact self-ballasted fluorescent lamp including an arc tube composed of a glass tube at least partially bent and electrodes with filament coils sealed at both ends of the glass tube, and a holder having insertion openings and holding the arc tube by fixing the ends of the glass tube inserted through the insertion openings.
(2) Related Art
In the present energy-saving era, compact self-ballasted fluorescent lamps have been increasingly widespread as energy-saving light sources alternative to incandescent lamps. As one example, a compact self-ballasted fluorescent lamp includes an arc tube formed by winding a glass tube in a double-spiral shape and enclosing mercury in the glass tube, a holder holding the arc tube, an electronic ballast contained in the holder for lighting the arc tube, a globe covering the arc tube, and a screw-type base attached to the holder.
At both ends of the glass tube, electrodes with filament coils are sealed. The holder has a pair of insertion openings through which the ends of the glass tube are inserted in the holder. Some compact self-ballasted fluorescent lamps have such a construction where the arc tube is held by the holder in a state where the filament coils placed in the glass tube are positioned within the holder (see Japanese Laid-Open Patent Application No. H8-339780). To efficiently obtain visible light emitted from the arc tube, however, compact self-ballasted fluorescent lamps having such a construction where the filament coils are positioned outside the holder have been developed in recent years.
Compact self-ballasted fluorescent lamps with the construction where the filament coils are positioned outside the holder can feature an improved amount of light emission. After the cumulative lighting time of long hours, however, these lamps start to suffer from poor rising characteristics at the lighting startup compared with the initial stage of their use.
FIG. 1 shows the relationship between a relative luminous flux value and an elapsed lighting time for a conventional compact self-ballasted fluorescent lamp. The relative luminous flux value is a luminous flux value relative to a luminous flux value during the steady lighting state, at the lighting startup of the conventional compact self-ballasted fluorescent lamp. Here, the conventional compact self-ballasted fluorescent lamp is repeatedly made ON and OFF with its base being oriented upward, until a total lighting time reaches 100 hours and 6000 hours. The total lighting time is a total of ON times when a ON/OFF cycle of “two hours and 45 minutes ON” and “15 minutes OFF” is repeated.
As shown in the figure, for the conventional compact self-ballasted fluorescent lamp, the time required by the relative luminous flux value during the steady lighting state to reach 60% is about 7.5 seconds for the total lighting time of 100 hours, whereas the time is about 20.5 seconds for the total lighting time of 6000 hours. The time required by the relative luminous flux value to reach 60% for the total lighting time of 6000 hours is 2.7 times as long as that for the total lighting time of 100 hours. In this way, after the total lighting time of long hours, the lamp starts to suffer from poor rising characteristics at the lighting startup compared with the initial stage of its use.